Two African waves that may develop
Hello everyone, it's Jeff Masters back with you again after a long stretch of vacation. Now that the peak part of hurricane season is upon us, I'll be with you every day for the next few months, in what promises to be an unusually active Atlantic hurricane season. We've got several threats to talk about today, most notably a strong African wave near 12.5°N 30.5°W, about 400 miles west-southwest of the Cape Verde Islands. This system, dubbed Invest 92L by NHC, is moving west to west-northwest at 10 - 15 mph, and has the potential to develop into a tropical depression or tropical storm before arriving near the northern Lesser Antilles Islands early next week. Recent visible satellite loops show that 92L is beginning to develop a surface circulation, and heavy thunderstorms are slowly building along the western edge of the center. However, a separate area of heavy thunderstorms lies 400 miles to the east, just south of the Cape Verde Islands, and this blob is interfering with consolidation of the center near the blob of heavy thunderstorms at 30.5°W. Water vapor satellite loops show that a large area of dry air from Africa lies just to the west of 92L, but the atmosphere in the immediate vicinity of 92L is moist, so dry air is currently not a problem for the storm. The SHIPS model is diagnosing low shear, 5 - 10 knots, over 92L, but the University of Wisconsin CIMSS analysis shows that moderate shear of 10 - 20 knots is affecting 92L. Sea surface temperatures are 26.5° - 27°C, which is very close to the 26.5°C threshold usually needed to support a tropical storm.
Figure 1. Noon satellite photo of Invest 92L.
Forecast for 92L
Low to moderate wind shear of 5 - 15 knots is predicted along 92L's path over the coming three days, which should allow the storm to steadily organize, assuming it can shut out any incursions of dry air that might intrude. The latest 00Z and 06Z model runs of the four best models for predicting tropical storm formation (GFS, ECMWF, NOGAPS, and UKMET) show little or no development of 92L, and NHC gave 92L just a 20% chance of developing into a tropical depression by Friday morning in their 8am outlook. Given the recent improvement in the satellite appearance of 92L, I would put these odds at 30%. A steady west to west-northwest motion for 92L is predicted by all of the models, which would put the storm in the vicinity of the northern Lesser Antilles Islands by Sunday. On Saturday and Sunday, 92L is expected to enter a region where an upper-level low pressure system will bring high wind shear of 20 knots to the storm, which should slow development. This upper-level low is also expected to turn 92L more to the northwest, so the storm may pass north of the Lesser Antilles. It is too early to know if 92L will recurve out to sea and potentially threaten Bermuda, or continue to the northwest towards the U.S. East Coast.
Figure 2. NASA MODIS image taken at 10:40am EDT 8/10/11 of the tropical wave emerging from the coast of Africa. The GFS model is predicting this system will develop into a tropical storm early next week. Image credit: NASA.
Tropical wave emerging from the coast of Africa
A strong tropical wave currently emerging from the coast of Africa near 8°N has a modest amount of spin and heavy thunderstorm activity associated with it, and has the potential to develop early next week once it moves past the Cape Verde Islands. The GFS model has been developing this system into a tropical storm in several of its recent runs. A westerly track towards the Lesser Antilles is expected by the GFS model.
Jeff Masters
Reader Comments
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Thinking the same exact thing. +1
Unwise to make any sort of judgement like that right now. Way to far out.
Regardless, I believe 93L is going to develop before 92L. I like the environment 93L is in more than the one 92L has to endure. Need to look at visible in the morning to see where the low level center is for 92L now. All of the convection in the ITCZ is probably going to attempt to pull it there.
any way have a good night well see whats 92 and 93L looks like in the AM
actually is quite weaker
00z
also i believe what is now 92L will miss the east coast in this run of gfs based on position of trough. still too early to tell though
Comment about what?
What happened?
92L's northern-western half is going to dissipate, conolidate, or move off to the north and split. the SE portion is more promising for developent currently.(near 10N)
strength of high in 00z gfs
Ohh, yeah.. Does look strong.. Though this is the pattern. Not surprising to see models show a strong ridge.
The best 850mb vort is in between the two areas of convection. However, I agree that the northern one is going to spin away and dissipate as it is more mid level in nature.
shows a stronger and more far south trough though and the orientation of strong ridge shears 92L by 132 hours
I dont like a fairly strong high where I am sitting in the NE Caribbean.
Well 92L recurves, but lets see if the ridge builds back in.. Remember when a storm recurves, the next one recurves further westward. Great example of that was Edwouard and Fran in 1996.
Still too much time ahead, but maybe.... may look like that in some models...
yes but looking at pattern a recurve is highly likely in 00z
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